The U.S. Computer Emergency Readiness Team warned this week of a security flaw in a popular tool intended to make it easier to add additional devices to a secure Wi-Fi network.

On Tuesday, the organization, known as US-CERT, cited findings from security researcher Stefan Viehbock, who uncovered the security hole in the so-called Wi-Fi Protected Set-up, or WPS, protocol, which is often bundled into Wi-Fi routers. The WPS protocol is designed to allow unskilled home users to set up secure networks using WPA encryption without much hassle. Users are then able to type in a shortened PIN instead of a long pass-phrase when adding a new device to the secure network.

That method, however, also makes it much easier for hackers to break into a secure Wi-Fi network, US-CERT says. The security threat could affect millions of consumers, since the WPS protocol is enabled on most Wi-Fi routers sold today.

"A few weeks ago I decided to take a look at the Wi-Fi Protected Setup (WPS) technology," Viehbock said in a blog post. "I noticed a few really bad design decisions which enable an efficient brute force attack, thus effectively breaking the security of pretty much all WPS-enabled Wi-Fi routers. As all of the more recent router models come with WPS enabled by default, this affects millions of devices worldwide."